Background <p>Parent-focused treatments are a promising approach for addressing youth anxiety outside of traditional therapist-delivered modalities. Supportive Parenting for Anxious Childhood Emotions (SPACE) has preliminarily demonstrated efficacy for reducing family accommodation (FA), a key treatment outcome for youth anxiety.</p> Objective <p>Since the mechanisms of SPACE remain relatively understudied, we examined youth-reported distress tolerance (DT), anxiety sensitivity (AS), and negative automatic thoughts as candidate mechanisms of SPACE using data from a previously conducted clinical trial.</p> Methods <p>In a sample of <i>N</i> = 68 youth (<i>M</i>_<i>age</i> = 10.2; 52% male; 62% White), we examined: (a) associations among candidate mechanisms and FA at baseline, (b) pre- to post-intervention change in candidate mechanisms, and (c) the association between pre- to post-intervention changes in candidate mechanisms and FA at post-intervention.</p> Results <p>Youth-reported DT, AS, and negative automatic thoughts were correlated with one another, but were not associated with parent-reported FA at baseline. These findings were inconsistent with youth-reported FA, which evidenced significant relations with DT and AS at baseline. Scores of candidate mechanisms slightly improved from pre- to post-intervention, with AS evidencing the most prominent reduction, although effect sizes were small. Finally, only salutary pre- to post-intervention changes in DT and social-based negative automatic thoughts were associated with parent-reported FA at post-intervention, suggesting the potential relevance of these variables as putative mechanisms in SPACE.</p> Conclusions <p>While our results do not permit definitive conclusions concerning the underlying youth-level mechanisms of SPACE, our findings may inform further refinement of parent-led interventions for anxious youth.</p>